The postnatal development of adrenergic receptor mechanisms is being studied in piglets. Work in progress consists of the analysis of cardiovascular responses to direct electrical stimulation of lumbar sympathetic efferents to the hindlimb. Adult control experiments will be carried out on mature minature swine. The responses under study include arterial pressure and femoral blood flow, while cardiac function (heart rate and left ventricular pressure) and renal blood flow are monitored. Strain gauge pressure transducer and electromagnetic flowmeter recordings provide data for the stimulus-response relationship to increasing frequency and intensity of nerve stimulation. The existence of age-dependency for any difference in magnitude of cardiovascular response to nerve stimulation is being established statistically in 5 age groups of animals less or minus to 1 day, 2-4 days, 1 week, 2 weeks, mature). The type of adrenergic mechanism involved is established pharmacologically through the use of receptor blocking agents. This research is expected to provide knowledge on the participation of the femoral circulation in the autonomic regulation of cardiovascular function in the neonate. BIBLIOGRAPHIC REFERENCES: Buckley, N.M., Gootman, P.M., Frasier, I.D. and McLean, C. Circulatory effects of renal sympathetic nerve stimulation in newborn piglets (abstract) Circula. 53/54: II-82, 1976. Buckley, N.M., Gootman, P.M., Gootman, N., Reddy, G.D., Weaver, L.C. and Crane, L.H. Age-dependent cardiovascular effects of afferent stimulation in neonatal pigs. Biol. Neonate, in press, 1976.